Cellulose nitrates are often used e.g. as film-forming agents in wood varnishes, printing inks, nail varnishes and leather coatings. Because of their hydrophobic properties, they are predominantly employed in organic solutions, leading to considerable environmental pollution. Neutral cellulose nitrates according to the prior art are conventionally only introduced into aqueous systems together with volatile organic solvents with the input of energy by emulsifying, which leads to environmental pollution that is unacceptable today.
Systems are also known in which cellulose nitrates without any further chemical modification are used in aqueous systems. In DE 27 03 075, for example, an aqueous coating composition dispersion is described which contains cellulose nitrate, alkyd resin, plasticiser and a polymeric emulsifier. In DE 30 07 936, aqueous dispersions of polyacrylates, cellulose esters (preferably cellulose nitrate), plasticisers, emulsifiers and fatty acid-modified resins are described.
However, these always exhibit not inconsiderable proportions of emulsifiers and other additives, which stabilise the emulsions. These additives generally entail disadvantages. If the emulsifiers are polymeric compounds, the dispersions are often highly viscous, which causes substantial impairment of the application properties. If, on the other hand, low-molecular-weight emulsifiers are used, these can escape from the coating, which can lead to health problems and environmental pollution.
The dispersions according to DE 30 07 936, on the other hand, still contain considerable quantities of organic solvents (cf. Example 1 in DE 30 07 936).
A need still existed, therefore, for cellulose nitrate derivatives that form stable aqueous dispersions without the addition of emulsifiers and organic solvents.
Surprisingly, it has now been found that this object is achieved by cellulose nitrate derivatives that can be produced by esterification of cellulose nitrate with dicarboxylic anhydrides and have a degree of substitution of the acid group (DS(acid)) in the range of 0.01–0.2 and a nitrogen content of 10.0% to 12.3%.
The production of some cellulose nitrate derivatives with anionic side groups is already known.
In DE 42 3 8453, binder compositions are described which contain polysaccharide nitrates with hydrophilic functional groups. The polysaccharide nitrates are produced by nitration of anionic polysaccharides and contain 0.2 to 1.5 hydrophilic groups per anhydroglucose unit. The binder compositions described require the use of 1–45 wt. % organic solvents, however.
In RU 2170235, the production of cellulose nitrate phthalate by esterification of cellulose nitrate with phthalic anhydride is described. However, there is no mention of an improvement in dispersibility due to the esterification or of a use of the cellulose nitrate derivative in dispersions.
In JP 63-135401, cellulose nitrate derivatives are described which are produced by esterification of cellulose nitrate with maleic anhydride. The products can be used as binders for magnetic coatings.